The present invention relates to a process for measuring the state of degradation of oils or fats. Also disclosed is a device for measuring the state of degradation of oils or fats.
The significance of the preparation of food with the aid of hot oils or fats is gaining importance amongst the public. Through the use of these hot substances, the cooking time for the preparation of many dishes is significantly shortened in comparison to other processes. In addition, the fats or oils used in the preparation may be used over a longer period of time for the cooking of larger amounts of food since the consumption of the hot oil in deep-frying is relatively small. However, this advantage of longer use of oils or fats also brings with it a disadvantage, since oils and fats, when used at the customary hot temperatures between approximately 90xc2x0 C. to 180xc2x0 C., are substantially changed in their composition i.e., decomposed or degraded.
The decomposition of oils and fats during the cooking process, essentially take place through the oxidation of the oil or the fat, during which many undesired chemical products arise such as, for example, polymers or free fatty acids. These undesired products negatively affect the taste of the prepared dishes, and also have a negative effect on the quality of the deep-fried food with respect to the health of the consumer.
It is therefore necessary to replace the oils and fats used for human consumption regularly and in a timely manner in order to avoid the negative effects on the consumer. In practice however, the oils and fats are replaced too early or too late. The criteria for the replacement are, in practice, frequently of a subjective nature, where replacement of the oil or fat is usually carried out according to time criteria or based on a visual or olfactory change in the oil or fat.
In order to be able perform the replacement of oils and fats in a timely manner, it is necessary to determine the quality of the fat according to objective criteria, i.e., when the decomposition of the fat or oil has progressed so far thereby requiring replacement.
The prior art (U.S. Pat. No. 3,739,265) provides a process and a device which provide for examining the oil for its electrical properties, in particular its dielectric properties. For this purpose, the measuring device has a receiving space in the form of a key which has disposed at its base a sensor formed as a capacitor. For the measurement, a certain amount of oil is applied to the sensor and the capacitance measured with this system is processed in an electrical circuit. As a result a measured value is obtained which provides information concerning the degree of decomposition of the fat. For this, a comparison is carried out between the fat or oil to be tested and a standard liquid which is also measured in an additional measuring process, usually beforehand. The dielectric constant, or change of the dielectric constant, which the sensor determines in the process, is a measure for the degree of decomposition of the fat or oil.
EP 1 046 908 A2 teaches a process and a device for measuring the state of oils or fats by measuring an electrical property of the oil or fat, using a measuring head that is disposed on an attachment of the measuring device. This is suitable for dipping into the hot fat or oil, e.g., in a deep-fat fryer, during operation in order in so doing to measure the capacitive properties of the oil.
U.S. Pat No. 3,739,265 teaches an instrument which requires the oil to be filled into a receiving device prior to measurement, for which purpose the oil must first be removed from the deep-fat fryer. Subsequently, the electrical properties of the oil or fat are measured in the device. For determining the state of the oil or fat, this device is not suitable for use in practice, i.e., even during the time when a kitchen is in operation. In particular, the complexity of the handling technology and the expenditure of time do not allow for practical application.
The device disclosed in EP 1 046 908 A2 is suitable for measuring the state of the oil directly during the operation, for example, of a deep-fat fryer. For this purpose, the sensor, which is disposed on an attachment of the device, is dipped directly into the hot oil or fat. After the dipping it is necessary for the exact determination of the measured value, and also for the determination of the temperature of the oil, to wait a certain time until a measurement providing information can be performed. The electrical connection between the sensor and the evaluation electronics occurs via cable laid free in the interior of the attachment.
xe2x80x9cIt is an object of the present invention to provide a process for measuring the state of degradation of oils and fats in order to make the process and device more suitable for use in practice and, in particular, to shorten the measuring time, to improve the result of the measurement, and to minimize the variability of the measurement. An embodiment of the invention provides a device for measuring the state of degradation of oil or fat comprising a sensor for measuring an electrical property of the oils or fats, wherein the sensor is mounted on a carrier and is connected to measurement electronics via one or more electrical leads, and further comprising a housing for evaluating or displaying the result of the measurement, wherein at least one of the electrical leads is disposed on a carrier part.xe2x80x9d
It is also an object of the present invention to provide a device for measuring the state of degradation of oils and fats. An embodiment of the invention provides a process for measuring the state of degradation of oil or fat comprising, measuring the dielectric constant of oil or fat with a sensor, wherein the sensor is brought into contact with the oil or fat in a liquid state, wherein the sensor is at a lower temperature than the oil or fat, and the dielectric constant of the oil or fat is measured while the sensor is adapting to the temperature of the oil or fat.